1. Field of the Invention
The present invention relates to a rotary piston engine and, more particularly, a method of and a device for supplying fuel to a stratified combustion rotary piston engine.
2. Description of the Prior Art
In the so-called Wankel-type rotary piston engine which comprises a casing composed of a rotor housing having a trochoidal inner peripheral surface and side housings which close opposite sides of said rotor housing and a polygonal rotor adapted to rotate eccentrically in said casing with apex portions thereof sliding over said inner peripheral surface, the flame initiated from an ignition plug propagates very swiftly toward the leading side located at the front side of the rotor as seen in the rotational direction of the rotor due to the flow of fuel-air mixture caused by the rotation of the rotor. However, the propagation of the flame toward the trailing side located at the rotationally rear side of the rotor is relatively impeded, whereby there exists the problem that although the fuel-air mixture is favorably combusted in the leading side, the combustion is incomplete in the trailing side thereby lowering the combustion efficiency with the results of increasing the fuel consumption and simultaneously increasing the emission of harmful uncombusted components such as HC and CO in the exhaust gas. In order to solve this problem, I have proposed a rotary piston engine having a first intake port which opens in said trochoidal inner peripheral surface and a second intake port which opens in an inner surface of said side housing at a position advanced from said first intake port with respect to the rotational direction of the rotor. The first intake port is supplied a fuel-air mixture while said second intake port is supplied with only air, thereby providing stratified charging in a manner that the leading side portion of the combustion chamber where the combustion of the fuel-air mixture is relatively easily effected is filled with a relatively rich fuel-air mixture, whereas the trailing side of the chamber where the combustion of fuel-air mixture is difficult to achieve is filled with only air.
In this stratified combustion rotary piston engine, the particular manner of combustion improves the fuel consumption when compared with the conventional rotary piston engine and, simultaneously, contributes to reducing the emission of HC and CO in the exhaust gas. However, since the emission of HC and CO is not completely reduced to zero, it is required that those components remaining in the exhaust gas are processed in a thermal reactor. Since it is required that temperature of the exhaust gas must be above a certain level if an effective operation of the thermal reactor is to be accomplished, the lowering of the exhaust gas temperature in the abovementioned stratified combustion causes the problem that the purifying performance of the thermal reactor is substantially lowered.
Furthermore, although the amount of NOx contained in the exhaust gas of the rotary piston engine is very small when compared with the reciprocating engines so that it meets with the present-day regulations for emission control without any countermeasures being required, it is expected that the regulations regarding exhaust gas will become more severe in the near future and, therefore, the current rotary piston engine will soon violate the regulations with regard to NOx emission.
It is known that generally there exists a relation such as shown in FIG. 1 between the air/fuel ratio and the emission of HC, CO and NOx in the exhaust gas of a gasoline engine. In FIG. 1 the scales for CO, HC and NOx are particularly adapted for the case of the rotary piston engine. As apparent from FIG. 1, the NOx content in the exhaust gas is a maximum when the air/fuel ratio is about 15-16, but and lowers relatively steeply as the air/fuel ratio increases or decreases from the abovementioned value. The present anti-air pollution rotary piston engine employs an air/fuel ratio of about 12-13, whereby the emission of NOx is restricted within an acceptable limit while the HC and CO delivered in this operational condition are eliminated by recombusting in a thermal reactor. However, if, for example, the limit value of 0.25 g/km for NOx, which is expected to be enforced in the near future, is to be satisfied, the NOx content must be lower than 130 ppm. To accomplish this, the air/fuel ratio must be either substantially low, that is, in the order of about 11-12 or, on the contrary, must be relatively high, that is, in the order of about 18-19. If the air/fuel ratio is lowered to the order of about 11-12, the amount of HC and CO substantially increases beyond the limit which can be processed by the present thermal reactor or catalyst. On the other hand, if the air/fuel ratio is increased as high as about 18-19, the ignitability of fuel-air mixture becomes poor thereby causing misfiring and making it difficult to maintain a smooth operation of the engine. In this condition, the CO content is almost zero and, although the amount of HC relatively increases when compared with its minimum value, its absolute value is still acceptable and it is still possible to process the uncombusted components by the present thermal reactor or catalyst.